Add sorted_unique ctor to sorted_vector_set and sorted_vector_map
Add sorted_unique ctor to sorted_vector_set and sorted_vector_map

Summary: [Folly] Add `sorted_unique` ctor to `sorted_vector_set` and `sorted_vector_map`. The `presorted` ctors are used with presorted but not necessarily unique inputs, so uniquify the inputs in that ctors. The untagged ctors which take a backing container presort but do not uniquify the backing container, so switch to presorting and uniquifying.

Reviewed By: vitaut

Differential Revision: D15215677

fbshipit-source-id: bf920103cfb6c297c186e5389701c08218dbc4b9

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly